There are many forms of conveyor mechanisms for transporting materials from one position to another and the choice of conveyor mechanism is affected by many factors including the physical nature of material to be conveyed, the horizontal and/or vertical distances to be traversed, capital cost, on-going maintenance costs and the like.
While there is a wide range of conveyors available for horizontal or slightly inclined transportation paths, there are relatively few forms of conveyor available for elevation of materials along an upright transportation path falling within the range of from, say, 45° to a horizontal datum to 90° or perpendicular to a horizontal datum. Even then, the suitability of a conveyor or elevating system is often dictated by the nature of the materials to be handled. Where floor space requirements are not critical, tubular screw augers may be used to elevate flowable particulate materials such as cereal grains through an angle of from about 30 to 40 degrees and a multiplicity of screw augers located on vertically spaced landings is required to elevate the grain over any significant height. Where floor space is more critical, bucket elevators are often employed. For very fine or low mass particulate materials, pneumatic conveyors may be used to good effect.
Several major shortcomings are apparent in conventional materials elevators utilized in the field of foodstuffs handling. Many foodstuffs such as potato crisps are highly fragile while others such as soy beans, freeze dried coffee granules are easily damaged even with the gentlest handling. Pneumatic conveying of aggressively abrasive particulate material such as foundry sands gives rise to very high maintenance costs due to wear, particularly in the region of conveyor ducts, where a change of direction is required.
Generally speaking, the difficulties encountered in the elevation of flowable materials has led to custom designed conveyor/elevator systems or otherwise an unsatisfactory compromise with apparatus not particularly suited to the materials being transported or the environment in which the elevating apparatus is required to operate.
Conventional screw augers, even when inclined at an angle of less than 45° to a horizontal datum are known to damage many particulate materials due to pressurization in the auger barrel with the accumulation of finely crushed detritus making it difficult to maintain cleanliness. Vertical or near vertical operation of a conventional screw auger appears to be unknown because of extreme pressure build up within the auger barrel due to friction and this in turn leads to excessive power requirements. Depending upon the clearance between the screw flight and the inner wall of the auger barrel, backflow will occur with larger clearances while crushing of the particulate material with excessive screw and barrel wear will occur with small clearances.
For any long screw augers, it is necessary to support the rotatable screw with “hanger” bearings at spaced intervals within the auger tube. A hanger bearing is located centrally of the auger tube by radially extending brackets and the bearings each support the auger shaft in a region of discontinuity in the auger flight necessitating a “back pressure” to feed material across the discontinuity gap to the next auger flight.
It is known to operate a screw auger type conveyor wherein the barrel is rotatable, at least partially relative to the auger screw.
U.S. Pat. No. 3,349,894 describes an inclined screw auger elevator for frangible materials such as potato or corn chips. The screw comprises a cupped helical flight with upturned outer edges and the tubular conveyor barrel rotates with the screw. Very careful attention must be paid to feed rates and screw rotational speed to avoid crushing of the frangible particulate material in use.
U.S. Pat. No. 3,279,592 describes a horizontal screw auger conveyor wherein the auger screw and the tubular barrel rotate together to avoid wear from relative rotation therebetween. A plurality of apertures along the barrel permit distribution of the particulate material to a multiplicity of delivery stations along the path of the conveyor.
U.S. Pat. No. 3,031,064 describes a horizontal screw auger conveyor having a split barrel wherein each barrel portion is selectively rotatable coaxially with the screw auger and each barrel is adapted to distribute particulate material at spaced delivery stations via hinged closures manually movable between a closed position and an open position under the influence of gravity by rotating a respective tube portion through about 180°.
Australian Patent Application 24574/77 discloses a horizontal screw auger having a helical slot formed in the tubular barrel. The tubular barrel is able to be rotationally oscillated in the same direction of rotation as the screw or counter thereto to selectively deposit material in an elongate delivery station beneath the auger barrel.
International Publication WO 95/26310 describes a feeder tube conveyor in the form of a horizontal screw auger with a plurality of inlet openings spaced helically about the portion of the tubular screw barrel located within a hopper of difficult to feed fibrous material. Associated with each inlet opening is an activator to disturb the fibrous material in the hopper above the screw barrel to prevent bridging of the material in the hopper. The auger barrel is rotatable with the screw but its direction of rotation may be reversed to clear blockages in the inlet openings.
German Patent Application DE 3 708 208 is concerned with a filling apparatus for thick pasty materials wherein a feed hopper and a tubular barrel are caused to rotate independently relative to a vertical stationary screw auger. The upper flight of the screw auger is shaped as a sweep to urge material into the mouth of the barrel and to flow downwardly therethrough.
U.S. Pat. No. 4,077,527 discloses an apparatus for horizontally transporting and dispensing a very fine particulate material wherein a conduit rotates about a stationary coil spring located within the conduit. The spring is fastened externally of a discharge end of the conduit and the inlet comprises a plurality of apertures in the conduit. The inlet communicates directly with a pressure fed hopper to receive a powdered feed of less than 50 micron particle size. The inlet end of the spring is allowed to float to permit axial extension of the spring under load.
It is an aim of the present invention to overcome or ameliorate at least some of the disadvantages associated with prior art elevating conveyors for flowable materials. As used herein, the expression “flowable materials” includes particulate materials, slurries, viscous liquids and the like but is not limited thereto.